Update TestRegisters for running on Linux (filed llvm.org/pr16301)
- skip the attach cases in TestRegisters.py -- caused slowness/sigabrt
- fixed log file removal function (in case test is run with -# flag)



git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@183812 91177308-0d34-0410-b5e6-96231b3b80d8