Revert "Move the scheduler to its own process"

Reverts saltstack/salt#17120

@cachedout @thatch45 When trying to track down problems with the tests on the develop branch, the test suite won't run locally. However, when I revert this commit, it runs just fine. I suspect it may be causing our develop branch test woes as well.

When I try to run the test suite, when it tries to set up the test daemons, I get the following information:
```
* Setting up Salt daemons to execute tests

Process Scheduler-1:2:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/root/SaltStack/salt/salt/master.py", line 112, in run
    time.sleep(self.schedule.loop_interval)
IOError: [Errno 22] Invalid argument
Process Scheduler-1:6:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/root/SaltStack/salt/salt/master.py", line 112, in run
    time.sleep(self.schedule.loop_interval)
IOError: [Errno 22] Invalid argument
Process Scheduler-1:7:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/root/SaltStack/salt/salt/master.py", line 112, in run
    time.sleep(self.schedule.loop_interval)
IOError: [Errno 22] Invalid argument
Process Scheduler-1:8:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/root/SaltStack/salt/salt/master.py", line 112, in run
    time.sleep(self.schedule.loop_interval)
IOError: [Errno 22] Invalid argument
Process Scheduler-1:9:
Traceback (most recent call last):
  File "/usr/lib/python2.7/multiprocessing/process.py", line 258, in _bootstrap
    self.run()
  File "/root/SaltStack/salt/salt/master.py", line 112, in run
    time.sleep(self.schedule.loop_interval)
IOError: [Errno 22] Invalid argument
```
It does that repeatedly until I hit `control c`. Note that I am running this on an Ubuntu 14.04 VM, which keeps timing out on the develop branch tests.

I ran the test suite with this commit reverted, and the testsuite ran successfully with no test failures.