ci: Add Pull request check to semaphore scripts

[Man-Jain]

This fixes the conditions of build failure when someone created a
pull request from the master branch. It now also checks if it is a
Pull request or not.

Fixes coala#583

Reviewers Checklist

• Appropriate logging is done.
• Appropriate error responses.
• Handle every possible exception.
• Make sure there is a docstring in the command functions. Hint: Lookout for
  botcmd and re_botcmd decorators.
• See that 100% coverage is there.
• See to it that mocking is not done where it is not necessary.

[codecov-io]

Codecov Report

Merging #2 into manank-patch-1 will not change coverage.
The diff coverage is n/a.

@@              Coverage Diff              @@
##           manank-patch-1     #2   +/-   ##
=============================================
  Coverage             100%   100%           
=============================================
  Files                  17     17           
  Lines                 349    349           
  Branches               62     62           
=============================================
  Hits                  349    349

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