test-lib: factor out $GIT_UNZIP setup

We set up the $GIT_UNZIP variable and lazy prereq in
multiple places (and the next patch is about to add another
one). Let's factor it out to avoid repeating ourselves.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

t/t0024-crlf-archive.sh

@@ -3,12 +3,6 @@
 test_description='respect crlf in git archive'
 
 . ./test-lib.sh
-GIT_UNZIP=${GIT_UNZIP:-unzip}
-
-test_lazy_prereq UNZIP '
-	"$GIT_UNZIP" -v
-	test $? -ne 127
-'
 
 test_expect_success setup '
 

t/t5003-archive-zip.sh

@@ -3,15 +3,9 @@
 test_description='git archive --format=zip test'
 
 . ./test-lib.sh
-GIT_UNZIP=${GIT_UNZIP:-unzip}
 
 SUBSTFORMAT=%H%n
 
-test_lazy_prereq UNZIP '
-	"$GIT_UNZIP" -v
-	test $? -ne 127
-'
-
 test_lazy_prereq UNZIP_SYMLINKS '
 	(
 		mkdir unzip-symlinks &&

t/test-lib.sh

@@ -750,3 +750,9 @@ test_lazy_prereq AUTOIDENT '
 # When the tests are run as root, permission tests will report that
 # things are writable when they shouldn't be.
 test -w / || test_set_prereq SANITY
+
+GIT_UNZIP=${GIT_UNZIP:-unzip}
+test_lazy_prereq UNZIP '
+	"$GIT_UNZIP" -v
+	test $? -ne 127
+'