Improved and fixed webclient mode.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13659 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Fix, fail if the tool is not CPAchecker and do not built CPAchecker.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13660 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
Fix: config.cloudMaster could be None.

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/trunk@13661 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c
merge from trunk

git-svn-id: https://svn.sosy-lab.org/software/cpachecker/branches/VariableTrackingPrecisionRefactoring@13663 4712c6d2-40bb-43ae-aa4b-fec3f1bdfe4c