SCHEMA-114. 'kiji install' can cause a NullPointerException.

"kiji install --kiji=kiji://!env/" triggers a NullPointerException.
This patch safeguards the "kiji install" and "kiji uninstall" commands
and prints a more useful error message.

Testing:
mvn clean verify (added new unit tests)
bin/kiji uninstall --kiji=kiji://.env/asdfasdf
bin/kiji uninstall --kiji=kiji://.env/
bin/kiji install --kiji=kiji://.env/