test-suite: pass the testng.configSuffix argument to TestNG
test-suite: allow configuration file suffix to be configurable

The default configuration file name is ".bioformats".  Setting the
testng.configSuffix property (e.g. to "stable") means that the preferred
configuration file is changed to (".bioformats." + testng.configSuffix), e.g.
".bioformats.stable".  If ".bioformats.stable" is not found, then
".bioformats" is still used.

This means that we can now do this in dev_4_4 Jenkins jobs:

ant -Dtestng.directory=/path/to/repo/ -Dtestng.configSuffix=stable test-automated

and then any dev_4_4-specific config files will be picked up.  That way,
changes on either branch that affect configuration can be made without
causing the other set of jobs to fail.
Merge pull request #673 from melissalinkert/config-file-suffix

Make configuration file suffix configurable