Revert dependency upgrades

[Kami]

Let's see if this helps with #3596 and #3595.

Update:
Fixes #3595

[Kami]

@armab

I managed to track down the memory usage issue to mongonegine 0.13.0. Upgrading to 0.13.0 doubles the memory usage, it's easy to replicate it (install latest dev packages, revert mongoengine to 0.11.0 or 0.12.0 and restart services, wait a bit for them to start up and check memory usage).

I will also go ahead and revert mongoengine upgrade for now and try to track down the actual place in mongoengine where it happens.

Great catch and thanks again.

[arm4b]

$ st2 --version
Traceback (most recent call last):
  File "/usr/bin/st2", line 7, in <module>
    from st2client.shell import main
  File "/opt/stackstorm/st2/local/lib/python2.7/site-packages/st2client/shell.py", line 34, in <module>
    from st2client.base import BaseCLIApp
  File "/opt/stackstorm/st2/local/lib/python2.7/site-packages/st2client/base.py", line 26, in <module>
    import urllib3
ImportError: No module named urllib3

[arm4b]

@Kami Taking into account ImportError: No module named urllib3, this code change from the pip upgrade PR should be reverted as well: https://github.com/StackStorm/st2/pull/3538/files#r128815747 So the package failure is valid.

I can confirm mongo memory fix.
Please also test if reverting requests fixes #3596 regression under EL7.

[Kami]

@armab Thanks for confirming and will do.