This reverts commit 66e7a38a.

Consistently invoke bash with /usr/bin/env bash in scripts to make code more portable (JIRA Ticket SPARK-817)

In some environments, this command

    export SPARK_HOME=$(cd "$(dirname $0)/.."; pwd)

echoes two paths, one by the "cd ..", and one by the "pwd". Note the resulting
erroneous -jar paths below:

    ctn@ubuntu:~/src/spark$ sbt/sbt
    + EXTRA_ARGS=
    + '[' '' '!=' '' ']'
    +++ dirname sbt/sbt
    ++ cd sbt/..
    ++ pwd
    + export 'SPARK_HOME=/home/ctn/src/spark
    /home/ctn/src/spark'
    + SPARK_HOME='/home/ctn/src/spark
    /home/ctn/src/spark'
    + export SPARK_TESTING=1
    + SPARK_TESTING=1
    + java -Xmx1200m -XX:MaxPermSize=350m -XX:ReservedCodeCacheSize=128m -jar /home/ctn/src/spark /home/ctn/src/spark/sbt/sbt-launch-0.11.3-2.jar
    Error: Invalid or corrupt jarfile /home/ctn/src/spark

Committer: ctn <ctn@adatao.com>

On branch master
Changes to be committed:

- Send output of the "cd .." part to /dev/null
	modified:   sbt/sbt

other issues

Conflicts:
	run2.cmd

executors per machine and remove the need for multiple IP addresses in
unit tests.

This does a few things to get this branch ready for release:

1. Upgrades the sbt and Scala version
2. Sets the release number to 0.5.1
3. Adds the Sonatype publishing target
4. Installs the PGP signing plugin
5. Removes the Mesos jar dependency

This reverts commit f58da616, reversing
changes made to 4449eb97.