[Yum] Fix rpmdb open failed error

Although not as good as other package managers, yum has come a long way since I last tried it.

However, due to me installing software using the rpm command and other graphical package managers (it is bad, seriously), I managed to screw up something causing it to complain with a "rpmdb open failed" error.

The fix is easy enough though:

rm -rf /var/lib/rpm/__db*

rpm --rebuilddb

yum clean all

yum update