gnu: Generalize the variable name of the test-only tzdata package.

* gnu/packages/base.scm (tzdata-2017a): Rename variable to tzdata-for-tests.
* gnu/packages/calcurse.scm (calcurse)[native-inputs, arguments]: Adjust
accordingly.
gnu/packages/glib.scm (glib): Likewise.
* gnu/packages/perl.scm (perl-libtime-parsedate): Adjust accordingly and
add tzdata-for-tests #:disallowed-references.
* gnu/packages/statistics.scm (r-minimal): Adjust accordingly.

gnu/packages/base.scm

@@ -1125,7 +1125,7 @@ and daylight-saving rules.")
 ;;; A "fixed" version of tzdata, which is used in the test suites of
 ;;; glib and R. We can update this whenever we are able to rebuild
 ;;; thousands of packages (for example, in a core-updates rebuild).
-(define-public tzdata-2017a
+(define-public tzdata-for-tests
   (package
     (inherit tzdata)
     (version "2017a")

gnu/packages/calcurse.scm

@@ -40,7 +40,7 @@
         "0il0y06akdqgy0f9p40m4x6arn66nh7sr1w1i41bszycs7div266"))))
     (build-system gnu-build-system)
     (inputs `(("ncurses" ,ncurses)))
-    (native-inputs `(("tzdata" ,tzdata-2017a)))
+    (native-inputs `(("tzdata" ,tzdata-for-tests)))
     (arguments
      ;; The ical tests all want to create a ".calcurse" directory, and may
      ;; fail with "cannot create directory '.calcurse': File exists" if run
@@ -49,7 +49,7 @@
        ;; Since this tzdata is only used for tests and not referenced by the
        ;; built package, used the "fixed" obsolete version of tzdata and ensure
        ;; it does not sneak in to the closure.
-       #:disallowed-references (,tzdata-2017a)
+       #:disallowed-references (,tzdata-for-tests)
        #:phases (modify-phases %standard-phases
                   (add-before 'check 'check-setup
                     (lambda* (#:key inputs #:allow-other-keys)

gnu/packages/glib.scm

@@ -171,9 +171,9 @@ shared NFS home directories.")
       ("python" ,python-wrapper)
       ("perl" ,perl)                              ; needed by GIO tests
       ("bash" ,bash)
-      ("tzdata" ,tzdata-2017a)))                  ; for tests/gdatetime.c
+      ("tzdata" ,tzdata-for-tests)))                  ; for tests/gdatetime.c
    (arguments
-    `(#:disallowed-references (,tzdata-2017a)
+    `(#:disallowed-references (,tzdata-for-tests)
       #:phases
       (modify-phases %standard-phases
         (add-before 'build 'pre-build

gnu/packages/perl.scm

@@ -9841,7 +9841,8 @@ in Perl source files.")
         (base32 "1lgfr87j4qwqnln0hyyzgik5ixqslzdaksn9m8y824gqbcihc6ic"))))
     (build-system perl-build-system)
     (arguments
-     `(#:phases
+     `(#:disallowed-references (,tzdata-for-tests)
+       #:phases
        (modify-phases %standard-phases
          ;; This is needed for tests
          (add-after 'unpack 'set-TZDIR
@@ -9851,7 +9852,7 @@ in Perl source files.")
              #t)))))
     (native-inputs
      `(("perl-module-build" ,perl-module-build)
-       ("tzdata" ,tzdata-2017a)))
+       ("tzdata" ,tzdata-for-tests)))
     (home-page "https://metacpan.org/release/Time-ParseDate")
     (synopsis "Collection of Perl modules for time/date manipulation")
     (description "Provides several perl modules for date/time manipulation:

gnu/packages/statistics.scm

@@ -119,7 +119,7 @@ be output in text, PostScript, PDF or HTML.")
                 "0r0cv2kc3x5z9xycpnxx6fbvv22psw2m342jhpslbxkc8g1307lp"))))
     (build-system gnu-build-system)
     (arguments
-     `(#:disallowed-references (,tzdata-2017a)
+     `(#:disallowed-references (,tzdata-for-tests)
        #:make-flags
        (list (string-append "LDFLAGS=-Wl,-rpath="
                             (assoc-ref %outputs "out")
@@ -244,7 +244,7 @@ be output in text, PostScript, PDF or HTML.")
        ("perl" ,perl)
        ("pkg-config" ,pkg-config)
        ("texinfo" ,texinfo) ; for building HTML manuals
-       ("tzdata" ,tzdata-2017a)
+       ("tzdata" ,tzdata-for-tests)
        ("xz" ,xz)))
     (inputs
      `(;; We need not only cairo here, but pango to ensure that tests for the