Add more debugging info on failures

[ying-sheng]

No description provided.

[ying-sheng]

There might be several things could be improved for debugging:
For example, if I run "Then the value of the cell in row 0, column 1 in the table with id "table_name" should be "first"":

• if the test failed, instead of "Assertion Failed: Cells do not match", could it be "Assertion Failed: Cells do not match. The value of the cell in row 0, column 1 in the table with id "table_name" is "second"", or something similar
• Or one can write "Print the value of the cell in row 0, column 1 in the table with id "table_name"" to get the value out