[analyzer] Put more uniqueness in scan-build's temporary directory names.

This is necessary when running two scan-build processes in parallel. The
directory naming scheme is now:

  yyyy-MM-dd-HHmmss-PID-N
  2013-09-13-174210-123-1

where "PID" is the scan-build process ID, and "N" is a sequential counter
(not likely to be needed now that seconds are mangled in, but just in case).

PR17196, using a suggested fix from Greg Czajkowski!

llvm-svn: 190735