BaseTools: Explicitly close files after readlines

BaseTools: Explicitly close files after readlines

Rework some file open().readlines to open, readlines, close.
This prevents excessive file handles being open at the same time,
which may be a problem with alternative python environments.

Cc: Liming Gao <liming.gao@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Michael Johnson <michael.johnson@intel.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>