Collect logs from tests

After each test, and after class setups and teardowns, the BeakerLib
integration plugin now downloads log files fromthe remote masters
and submits them using rlFileSubmit.

Part of the work for: https://fedorahosted.org/freeipa/ticket/3621
Do not hardcode path to ipa-getkeytab in tests

Using the in-tree binary makes testing outside the source tree
impossible.
Use ipa-getkeytab from $PATH, and add the directory to $PATH when
running the in-tree tests.

Part of the work for https://fedorahosted.org/freeipa/ticket/3654
Flush stream after writing service messages

sys.stdout is buffered by default if redirected to a file.
This may causes automated installation to appear hung.
Flush the stream so that messages are written immediately.
Show logs in failed tests

Output from IPA's log manager is not captured by Nose's logcapture plugin.
Forward IPA logs to a regular Python logger so that they are shown
on failures.
IPA log messages are also shown on standard error.

Filter out Paramiko logs by default; these are too verbose.

Part of the work for: https://fedorahosted.org/freeipa/ticket/3621
tests: Allow public keys for authentication to the remote machines

Part of the work for https://fedorahosted.org/freeipa/ticket/3621
tests: Configure/unconfigure remote hosts

Set up the hostname, /etc/resolv.conf, and /etc/hosts on remote
hosts in the test setup.
Undo the changes in test teardown.

Part of the work for https://fedorahosted.org/freeipa/ticket/3621