NOLINT a few operator overloads, to enable whitespace/operators

Review: https://reviews.apache.org/r/19967
Enabled whitespace/operators rule for cpplint.

Enabled whitespace/operators rule for cpplint, which covers the following:
You should always have whitespace around binary operators.
Missing spaces around <, >, or =
We allow no-spaces around << when used like this: 10<<20, but
not otherwise (particularly, not when used as streams)
There shouldn't be space around unary operators

Review: https://reviews.apache.org/r/19967
Modify configure.ac to fix --with-sasl.

Fixes MESOS-1839.

Review: https://reviews.apache.org/r/26133
stout: Always use stout ABORT() rather than system abort()

This makes it so any time there is an abort, we get a line number and at least
a basic message as to why there was an abort. If you want a clean(er) exit, use
<stout/exit>.

Also adds an overload which takes a standard string and unwraps it to a
const char * automatically, since a lot of the time we are building strings
to pass them to abort.

Review: https://reviews.apache.org/r/26472
libprocess: Always use stout ABORT() rather than system abort()

This makes it so any time there is an abort, we get a line number and at least
a basic message as to why there was an abort. If you want a clean(er) exit,
use <stout/exit>.

Review: https://reviews.apache.org/r/26473