IMPALA-7460 part 1: require user to install Paramiko and Fabric

- Remove Fabric and Paramiko as requirements. They aren't needed by
  anything in buildall.sh.
- Add a means to install into the impala-python virtual environment by hand.
  impala-pip is fine for this.
- Add another requirements file for extended testing. The dependency
  situation is messy and untangling that out of impala-python and into
  lib/python should be out of the scope of IMPALA-7460.
- Update core tests, which cover real regressions that have happened in
  the past, to run against locations that don't require a Paramiko
  import. This moves some logic out of concurrent_select.py into a
  thinner module.
- Insulate ssh_util from globally-scoped import so that it only imports
  when needed.

Testing:
- This works in my development environment.
- This works in my downstream stress and query gen environments.
- This works when doing a full data load.
- Impala still builds on a variety of OSs.

Todo:
- A subsequent review will update the versions.

Change-Id: Ibf9010a0387b52c95b7bda5d1d4606eba1008b65
Reviewed-on: http://gerrit.cloudera.org:8080/11264
Reviewed-by: Michael Brown <mikeb@cloudera.com>
Tested-by: Impala Public Jenkins <impala-public-jenkins@cloudera.com>

infra/python/deps/compiled-requirements.txt

@@ -19,10 +19,6 @@
 # after the toolchain is bootstrapped. Installed after requirements.txt
 
 argparse == 1.4.0
-Fabric == 1.10.2
-  paramiko == 1.15.2
-    ecdsa == 0.13
-  pycrypto == 2.6.1
 impyla == 0.14.0
   bitarray == 0.8.1
   sasl == 0.1.3

infra/python/deps/extended-test-requirements.txt

@@ -0,0 +1,24 @@
+# Licensed to the Apache Software Foundation (ASF) under one
+# or more contributor license agreements.  See the NOTICE file
+# distributed with this work for additional information
+# regarding copyright ownership.  The ASF licenses this file
+# to you under the Apache License, Version 2.0 (the
+# "License"); you may not use this file except in compliance
+# with the License.  You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+
+# Requirements for use of test tooling (tests/comparison and tests/stress).
+
+# IMPALA-7460 TODO: upgrade Fabric and Paramiko
+Fabric == 1.10.2
+  paramiko == 1.15.2
+    ecdsa == 0.13
+  pycrypto == 2.6.1