Support testing commit-msg hook from JAR

Some build systems may choose to pass off a JAR containing
all resources under test rather than a directory of tests
(e.g. Buck). Support testing under those environments by
copying the script to a temporary file and removing said
file after the test is done.

Change-Id: Idf1f07546b0a5b523b314f1085b7e0123e0cb502
1 file changed