Support history in phutil_console_prompt()

Summary:
I've tried several approaches, this is the only one which works for me:

• There's almost no chance that readline() will be available in PHP so I don't even check it.
• I wasn't able to convince execx() to read the input.
• I wasn't able to convince phutil_passthru() to give me the $REPLY or output.
• Good old shell_exec() works.

I'm not sure if read -p supports colors but they are not much useful here.
I need to use read -p instead of echo otherwise the prompt is cleared with scrolling.

Test Plan:

phutil_console_prompt('Write:', '/tmp/history-test');

• Run several times.
• Input different strings.
• Scroll in history.
• Provide empty input.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Koolvin

Differential Revision: https://secure.phabricator.com/D2579