Handle errors in individual controllers

[narrieta]

Added try/except to _for_each_controller

---

PR information

• The title of the PR is clear and informative.
• There are a small number of commits, each of which has an informative message. This means that previously merged commits do not appear in the history of the PR. For information on cleaning up the commits in your pull request, see this page.
• Except for special cases involving multiple contributors, the PR is started from a fork of the main repository, not a branch.
• If applicable, the PR references the bug/issue that it fixes in the description.
• New Unit tests were added for the changes made and Travis.CI is passing.

Quality of Code and Contribution Guidelines

• I have read the contribution guidelines.

---

This change is 

[codecov]

Codecov Report

Merging #1570 into develop will not change coverage.
The diff coverage is 81.25%.

@@           Coverage Diff            @@
##           develop    #1570   +/-   ##
========================================
  Coverage    63.37%   63.37%           
========================================
  Files           78       78           
  Lines        11058    11058           
  Branches      1559     1559           
========================================
  Hits          7008     7008           
  Misses        3711     3711           
  Partials       339      339

Impacted Files	Coverage Δ
azurelinuxagent/common/cgroupapi.py	62.5% <81.25%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b581fdc...d766842. Read the comment docs.

[codecov]

Codecov Report

Merging #1570 into develop will not change coverage.
The diff coverage is 81.25%.

@@           Coverage Diff            @@
##           develop    #1570   +/-   ##
========================================
  Coverage    63.37%   63.37%           
========================================
  Files           78       78           
  Lines        11058    11058           
  Branches      1559     1559           
========================================
  Hits          7008     7008           
  Misses        3711     3711           
  Partials       339      339

Impacted Files	Coverage Δ
azurelinuxagent/common/cgroupapi.py	62.5% <81.25%> (ø)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update b581fdc...d766842. Read the comment docs.

[pgombar]

LGTM