Migrate non-components third parties into /appengine/third_party/.

Migrate non-components third parties into /appengine/third_party/.

The ones used by components are addressed differently.

- Minor reduction in sys.path hacking.
- Improve run_coverage filters to skip more external packages.

R=vadimsh@chromium.org
BUG=

Committed: https://code.google.com/p/swarming/source/detail?repo=default&r=ddef67a942ba0af3067ad1c778a4b03683113db6

[M-A, 2015-03-25 01:56:09]

That explicitly doesn't address components/components/third_party on purpose.

[vadimsh, 2015-03-25 01:59:35]

lgtm

[M-A, 2015-03-25 12:57:14]

Committed patchset #1 (id:1) manually as
ddef67a942ba0af3067ad1c778a4b03683113db6 (presubmit successful).