Add explicit project exclusion support

While it was previously possible to exclude projects with the 'projects'
keyword by creating a negative match regular expression, this required
all the excluded projects to be specified in a single ORed regex which
is very ugly and error prone. Instead, introduce an explicit keyword,
'excludeProjects', which may be specified more than once to handle
project exclusions in a straight forward manner.

Also, bump ReplicationIT test target timeout to long. It defaulted to
Bazel's 'moderate' timeout bucket (300s). With new test additions in
this change, it will reach that ceiling and fail with a timeout. Set
its 'timeout' to long (900s).

Release-Notes: Add explicit project exclusion support
Change-Id: I4e50f923f734537bc32b6a350d3268dbc286d818