dosep.py: Add ability to set default test timout based on target

Summary:
Current default is 10 minutes, which causes the test suite to run very long in
case of test timeouts. On local linux, each test completes in under 90 seconds in the
slowest configuration (debug build of lldb, using debug clang to build
inferiors). I am changing the default to 4m on local targets, while retaining
the 10m timeout for remote ones.

Reviewers: sivachandra, vharron

Subscribers: tberghammer, lldb-commits

Differential Revision: http://reviews.llvm.org/D10527

llvm-svn: 240946