Revert "make atomic_replace use shutil.copy2 instead of os.rename() so it will work across filesystems".

AR function was leaving some tmp files behind, want to revert, will have better implementation soon, this is the old way now.

This reverts commit f74a1fa4f0b1a928a85c1316dfceb42637624a2f.
clean up first_found to fix a few issues:

 - add a skip option so it won't raise an exception if you don't match anything
 - make it work as a drop-in replacement for first_available_file
 - document in the module comments all of the above cases
Merge pull request #2716 from skvidal/first_found_skip_fix

clean up first_found to fix a few issues:
Small spelling correction to authorized_key module docs
Merge pull request #2720 from base10/devel

Small spelling correction to authorized_key module docs
Remove an extra space in the module execution line if no environment was set.