CBQE-2115: set COUCHBASE_REPL_TYPE in install.py

tap is used by default - if environment var is set then we will use upr instead.
USAGE: python scripts/install.py -i hosts.ini -p product=cb,version=3.0.0-432,upr=True
TODO: windows

Change-Id: I524b7d06f228221f4320e1c7748c45cf64612686
Reviewed-on: http://review.couchbase.org/34400
Reviewed-by: Michael Wiederhold <mike@couchbase.com>
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Andrei Baranouski <andrei.baranouski@gmail.com>