Added rpm packages support for RHEL, CentOS and Scientific Linux
get_arch() properly returns arch or unknown, fixed require.rpm.repository to conver arch to str, refactored --enablerepo thanks to Ronan Amicel in require.rpm.install
fix unindent in rpm.install
fix unexpected indent in system.get_arch()
check if repos is actually passed so we dont iterate over NoneType object in rpm.install()
PEP 8 friendly, removed unused imports in require.rpm module
make sure the repo name is always lowercase in require.rpm.repo()
remove unneeded lower() call on repo name in require.rpm.repo(), as we're doing it early in the method
Merge pull request #73 from scalp42/rpm_support

CentOS/RHEL/SL support