Fix hold and release of a retrying task

Previously, on release, it will reset the task's state to `waiting`.
Run jobscript 00 test w/o global configuration

(The presence of global configuration can cause the job script to look
different.)
Merge pull request #1268 from matthewrmshin/fix-hold-release-retry

Fix hold and release of a retrying task
Run jobscript 00 test w/o global configuration

Part 2.
Merge pull request #1269 from matthewrmshin/fix-jobscript-00-conf

Run jobscript 00 test w/o global configuration
test-battery: don't hard code use of xxdiff

Allow use of new environment variable CYLC_TEST_DIFF_CMD to specify any
alternate `diff` command.
Fix hold-retry-release logic

Previously, on holding a suite with a submitted or a running task that
can retry, if the task fails while the suite is on hold, it will go into
retrying immediately instead of being held with the rest of the suite.
This change fixes the problem.
Merge pull request #1270 from matthewrmshin/remove-test-battery-xxdiff

test-battery: don't hard code use of xxdiff
Merge pull request #1271 from matthewrmshin/fix-hold-retry-release

Fix hold-retry-release logic