IMPALA-12825: Install thrift into the impala-python virtualenv

impala-python currently gets its Thrift from the toolchain
by adding the appropriate Thrift toolchain directories to
the PYTHONPATH. This is a problem when switching to Python 3,
because the toolchain Thrift was built with Python 2 and
this can produce complicated bugs. In general, it is also
not a good idea to get Python dependencies from the toolchain.

This switches to installing Thrift into the impala-python
virtualenv, which lets the different Python versions have
their own copy of compiled files.

Testing:
 - Ran a core job

Change-Id: Ib36e8a1ce8d446b69b08e81ea458f95c158e28f5
Reviewed-on: http://gerrit.cloudera.org:8080/21046
Reviewed-by: Michael Smith <michael.smith@cloudera.com>
Reviewed-by: Wenzhe Zhou <wzhou@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

infra/python/deps/requirements.txt

@@ -64,6 +64,7 @@ sqlparse == 0.3.1
 texttable == 0.8.3
 virtualenv == 16.7.10
 avro==1.10.2
+thrift==0.16.0
 
 # Required for Kudu:
   Cython == 0.29.14