added new play_hosts var

this variable has the 'current host list' to be executed over in the
play. Useful when using --limit to not iterate over hosts not included
in play in templates or with_items.

Signed-off-by: Brian Coca <briancoca+dev@gmail.com>
Merge pull request #5771 from bcoca/play_hosts2

added new play_hosts var
Updating changelog and docs for the new play_hosts variable
Make tmp paths in TestRunner dynamic based on pid

Fixes #4723
Create a common EC2 connection argument spec for EC2 modules

Refactor the currently well-factored ec2 modules (i.e. those that already use ec2_connect) to
have a common argument spec. The idea is that new modules can use this spec without duplication
of code, and that new functionality can be added to the ec2 connection code (e.g. security
token argument)
Merge pull request #5880 from willthames/ec2_modules_refactor

Create a common EC2 connection argument spec for EC2 modules
Micro-optimization of inventory.expand_hosts.detect_range
Micro-optimization: replace s.find(x)!=-1 with x in s

timeit shows a speedup of ~3x on Python 2.7.5 x86_64.
It also makes the code a bit shorter.
hostname module: don't filter hostnamectl with awk

There's no need to filter hostnamectl's output with awk because its man
page says:

    hostnamectl [OPTIONS...] {COMMAND}

       --static, --transient, --pretty
	   If status is used (or no explicit command is given) and one
	   of those fields is given, hostnamectl will print out just
           this selected hostname.

E.g. hostnamectl --static status => ansible.example.org