Clean up imports across the board in tp-qemu. The criteria
followed was:

1) Remove unnecessary imports
2) Turn multi imports from a single entry point to one
   import per line. This increases both patch and
   source code readability.
3) Separate blocks of imports with a line:
   * Python standard library imports
   * Autotest imports
   * virttest imports
   * Internal tp-qemu imports
4) Remove try/except blocks refering autotest libs and
   stick with the virttest.staging copy

This paves the way for the future removal of autotest
references, replacing those references with avocado ones.
Signed-off-by: NLucas Meneghel Rodrigues <lmr@redhat.com>