Stop using configs from the local tor install when we launch tor for tests

[teor]

We should stop using paths in /usr when we're launching tor for build tests.

We don't get full logs for all the tor processes we launch, but these scripts launch tor, so they're probably affected:

• test_rebind.sh
• test_key_expiration.sh
• test_keygen.sh
• test_zero_length_keys.sh

test-network.sh is also affected, but we'll deal with that in chutney in #29701.

For example, on my machine, test_rebind.sh does:

2019-03-05 11:00:11.573 Tor logged: "Mar 05 11:00:11.571 [notice] Configuration file "/usr/local/etc/tor/torrc" not present, using reasonable defaults.", waiting for "Opened Control listener on"
2019-03-05 11:00:11.596 Tor logged: "Mar 05 11:00:11.591 [notice] Parsing GEOIP IPv4 file /usr/local/share/tor/geoip.", waiting for "Opened Socks listener"
2019-03-05 11:00:11.899 Tor logged: "Mar 05 11:00:11.899 [notice] Parsing GEOIP IPv6 file /usr/local/share/tor/geoip6.", waiting for "Opened Socks listener"

[rl1987]

test_keygen.sh does the following:

 85 touch "${DATA_DIR}/empty_torrc"                                                 
 86                                                                                 
 87 QUIETLY="--hush"                                                                
 88 SILENTLY="--quiet"                                                              
 89 TOR="${TOR_BINARY} ${QUIETLY} --DisableNetwork 1 --ShutdownWaitLength 0 --ORPort 12345 --ExitRelay 0 -f ${DATA_DIR}/empty_torrc"

[rl1987]

So does test_key_expiration.sh; test_zero_length_keys.sh launches zero_length_keys.sh, which does this as well.

[rl1987]

Doing the same in test_rebind.py: ​https://github.com/torproject/tor/pull/793