Environment initialization for binaries

[dkrupp]

CodeChecker calls various binaries during analysis: clang, clang-tidy,
clang-extdef-mapping etc.
If the binary is delivered within the CodeChecker package,
LD_LIBRARY_PATH needs to be extended with it.

Otherwise the environment of the caller shell should be used
for excuting binaries.

[bruntib]

Great improvement, I like the idea of not trusting the callers to provide the environment to these functions.
Some further locations should apply this approach:

ctu_autodetection.py:78
  invoke_binary_checked
  
clangtidy/analyzer.py:145
  get_warnings
  
cppcheck/analyzer.py:243
  get_analyzer_checkers
  
gcc/analyzer.py:89
  get_analyzer_checkers

codechecker_analyzer/cmd/analyzers.py:123,126
  main

[dkrupp]

Thanks for the review. I added the environment initialization to the additional places.