Allow exclude_arch and exclude_os_type in qa-suite yamls

Adding the option:

exclude_arch:

or

exclude_os_type:

in the ceph-qa-suite yaml allows tests to be skipped for certain
types of hardware or distros.

Example:

exclude_arch: armv7l

This will make said test not run on arm machines.

exclude_os_type: rhel

Would make multi-distro tests skip a specific test on RHEL.
Do not run multiple tests (for distros) on baremetal.

Teuthology doesnt care about os_type for baremetal (ATM). This
change makes it so you can run tests that have been switched over
to run on multiple distros (on vms) on baremetal as well as all
non-ubuntu tests will be skiped (to avoid running the same test
multiple times on baremetal.

Signed-off-by: Sandon Van Ness <sandon@inktank.com>