Allow --opt-conf-key=KEY as environment variable.

Introduce ROSE_APP_OPT_CONF_KEYS and ROSE_SUITE_OPT_CONF_KEYS.
Program will read keys from the relevant environment variable
and then add the ones specified in each --opt-conf-key=KEY.

This fixes #384.
Merge branch 'master' into 384.rose.run.opt-conf-keys
rose.run: remove redundant `if` test.
Merge pull request #388 from matthewrmshin/384.rose.run.opt-conf-keys

rose *-run: allow --opt-conf-key=KEY as environment variable.