[SPARK-2608][Core] Fixed command line option passing issue over Mesos via SPARK_EXECUTOR_OPTS

This is another try after #2145 to fix [SPARK-2608](https://issues.apache.org/jira/browse/SPARK-2608).

The basic idea is to pass `extraJavaOpts` and `extraLibraryPath` together via environment variable `SPARK_EXECUTOR_OPTS`. This variable is recognized by `spark-class` and not used anywhere else. In this way, we still launch Mesos executors with `spark-class`/`spark-executor`, but avoids the executor side Spark home issue.

Quoted string with spaces is not allowed in either `extraJavaOpts` or `extraLibraryPath` when using Spark over Mesos. The reason is that Mesos passes the whole command line as a single string argument to `sh -c` to start the executor, and this makes shell string escaping non-trivial to handle. This should be fixed in a later release.

Classes in package `org.apache.spark.deploy` shouldn't be used as they assume Spark is deployed in standalone mode, and give wrong executor side Spark home directory. Please refer to comments in #2145 for more details.

Author: Cheng Lian <lian.cs.zju@gmail.com>

Closes #2161 from liancheng/mesos-fix-with-env-var and squashes the following commits:

ba59190 [Cheng Lian] Added fine grained Mesos executor support
1174076 [Cheng Lian] Draft fix for CoarseMesosSchedulerBackend

(cherry picked from commit 935bffe3bf6c91a42288bff8c1ec69fecb41a769)
Signed-off-by: Reynold Xin <rxin@apache.org>
[SPARK-3264] Allow users to set executor Spark home in Mesos

The executors and the driver may not share the same Spark home. There is currently one way to set the executor side Spark home in Mesos, through setting `spark.home`. However, this is neither documented nor intuitive. This PR adds a more specific config `spark.mesos.executor.home` and exposes this to the user.

liancheng tnachen

Author: Andrew Or <andrewor14@gmail.com>

Closes #2166 from andrewor14/mesos-spark-home and squashes the following commits:

b87965e [Andrew Or] Merge branch 'master' of github.com:apache/spark into mesos-spark-home
f6abb2e [Andrew Or] Document spark.mesos.executor.home
ca7846d [Andrew Or] Add more specific configuration for executor Spark home in Mesos