Explicitly specify encoding for open() calls

Explicitly specify encoding for open() calls

Address the following warnings reported by PyLint 2.10.2:

    ************* Module tests-checkds
    bin/tests/system/checkds/tests-checkds.py:70:9: W1514: Using open without explicitly specifying an encoding (unspecified-encoding)
    bin/tests/system/checkds/tests-checkds.py:120:13: W1514: Using open without explicitly specifying an encoding (unspecified-encoding)
    bin/tests/system/checkds/tests-checkds.py:206:17: W1514: Using open without explicitly specifying an encoding (unspecified-encoding)
    ************* Module yamlget
    bin/tests/system/digdelv/yamlget.py:22:5: W1514: Using open without explicitly specifying an encoding (unspecified-encoding)

(cherry picked from commit 6a4b8b145620a6532d334e26fd12427e9b9c7b8c)