rpm_build_info: 'rockstor' hardcoded in error

[chrstphrchvz]

In the rpm_build_info function, the rockstor package is hardcoded in one of the possible errors:

rockstor-core/src/rockstor/system/pkg_mgmt.py

Line 118 in f170ee5

logger.info('No "rockstor" package found: source install?')

Since the function is getting the package name from the pkg argument, pkg should be used in the error instead, even though the function is currently only used to check for the rockstor package.

[phillxnet]

@chrstphrchvz Agreed. Nice.
Thanks for your continued efforts in this part of the code. Much appreciated. Hopefully I can take a closer look at this soon. Unless @FroggyFlox beats me to it of course.