fix the rpm build for centos

[jdurgin]

See also ceph/googletest#1

Passed here (just had to edit the commit message, hence different sha1): http://gitbuilder.sepia.ceph.com/gitbuilder-ceph-rpm-centos7-amd64-basic/log.cgi?log=66fa1ddfbb9c040e89ae9aca4c56a410c6ff4f5c

[jdurgin]

@BlaXpirit had to pull in your commit to make this work in addition to the googletest fix - maybe because python3-devel etc. are now installed on the machine, and weren't there before wip-cmake-py3

In case anyone else has a branch that runs into this, the error without the python 3 virtualenv workaround is:

http://gitbuilder.sepia.ceph.com/gitbuilder-ceph-rpm-centos7-amd64-basic/log.cgi?log=983603ac2b3a4925e5c0760a625fbab0c00cdcbd

 Failed to import the site module
Traceback (most recent call last):
File "/srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/lib64/python3.4/site.py", line 67, in
import os
File "/srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/lib64/python3.4/os.py", line 616, in
from _collections_abc import MutableMapping

    Error: Import No module named '_collections_abc' 

Using base prefix '/usr'
New python executable in /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/bin/python3
Also creating executable in /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/bin/python

    ERROR: The executable /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/bin/python3 is not functioning 

    ERROR: It thinks sys.prefix is '/srv/autobuild-ceph/gitbuilder.git/build/src/ceph-detect-init' (should be '/srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3') 

    ERROR: virtualenv is not compatible with this system or executable 

Running virtualenv with interpreter /bin/python3
./install-deps.sh: line 150: /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/bin/activate: No such file or directory
Requirement already satisfied (use --upgrade to upgrade): setuptools>=0.8 in /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python2.7/lib/python2.7/site-packages
Requirement already satisfied (use --upgrade to upgrade): pip>=7.0 in /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python2.7/lib/python2.7/site-packages
Requirement already satisfied (use --upgrade to upgrade): wheel>=0.24 in /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python2.7/lib/python2.7/site-packages
./install-deps.sh: line 156: /srv/autobuild-ceph/gitbuilder.git/build/install-deps-python3/bin/activate: No such file or directory 

[ktdreyer]

@b-ranto is this going to cause problems in RH downstream builds where there is no internet access?

[b-ranto]

@ktdreyer Not necessarily, it just patches the pre-build phase. We might just have to ship our own version of virtualenv if the issue manifests itself in the RHEL build.