run tests_run in parallel

python pytest-xdist; we haven't been using this;
tests_run_all seem to fail with this (Swarming already)
add external cmake module to determin number for CPU cores
execute python unittests in parallel

pytest-xdist -n
Merge branch 'master' into parallel_unittests
Revert "add external cmake module to determin number for CPU cores"

This reverts commit f46362b6e31fd460d5149a812c4c36d2b11fac92.
Revert "execute python unittests in parallel"

This reverts commit a05f97b4013971e5cf0229b07b0ab018ed6bf3b6.
parallel tests: use harcoded 2 threads

not much improvement was observed otherwise.
Merge branch 'master' into parallel_unittests

Conflicts:
	CMakeLists.txt
fix mistake in merge
Moving pip requirements into archive.
Merge branch 'retry-pip-install' into archive-pip-requirements
Merge branch 'master' of github.com:numenta/nupic into archive-pip-requirements
Merge pull request #975 from rhyolight/archive-pip-requirements

Moving pip requirements into archive.
Merge branch 'master' into parallel_unittests
Minor changes in CMake file
Merge pull request #958 from breznak/parallel_unittests

Parallel unittests
Updates nupic.core to df86d7f6c61296a2524a86524f7db16d6a4d60fe.
Merge pull request #979 from numenta-ci/core-update-df86d7f6c61296a2524a86524f7db16d6a4d60fe

Updates nupic.core to df86d7f6c61296a2524a86524f7db16d6a4d60fe.
Updates nupic.core to 980c16afb45bd1625164b32413ea0992b965a63c.
Merge pull request #983 from numenta-ci/core-update-980c16afb45bd1625164b32413ea0992b965a63c

Updates nupic.core to 980c16afb45bd1625164b32413ea0992b965a63c.