Remove nested 'pxe' dict from driver_info

driver_info do not support nested objects. Self-namespace will be used
to distinguish parameters from one driver to another.

Change-Id: I165438fff7a032b54d3f019b727f6f85ad88d153
Partial-Bug: #1236533
Remove nested 'ssh' dict from driver_info

driver_info do not support nested objects. Self-namespace will be used
to distinguish parameters from one driver to another.

Change-Id: I2756abc855ddfd5388dacb083c12c8916beedd01
Partial-Bug: #1236533
Replace tearDown with addCleanup in unit tests

Infra team has indicated that tearDown should not be used, and should
be replaced with addCleanup in all places. This patch removes the
few cases of tearDown in Ironic.

Change-Id: Ie2a59ea018c68fccadf0530409255bd9a0cf9717
Merge "Remove nested 'ssh' dict from driver_info"
Merge "Replace tearDown with addCleanup in unit tests"