Implement folder input.

One flag '-f' corresponds to one directory that stores a parsed report.

Bug: 296988808
Test: ./compare_cts_reports.py -r test_result_1.xml [test_result_2.xml] \
    [-r report.zip] [-f parsed_dir_1/] [-f parsed_dir_2/] -m n -d output_dir/
Change-Id: I26310982dc8ef18f5dbfb1a8382ea3a600508fbe
2 files changed