fixed addTimestampToFile that was returning new filenames without the original filename

[beubanks]

Made change to RestPy/SampleScripts/loadQuickTest.py function addTimestampToFile:
restoring newFilename to the full newFileWithTimestamp in the addTimestampToFile function.
It was removed in commit 6a82f5e

[beubanks]

Hi @hubogee, is there anything else I should provide for this PR?
I have tested the change and it now includes the original file name in the new file name. For example, here the first three files are from a run with the original loadQuickTest.py and the last four are from a run with the modified:
`
[beubanks@beubanks-cs9-1 ixia-env]$ ls | grep 151323

rfc2544throughput_1trial_imix_151323.csv
rfc2544throughput_1trial_imix_151323.pdf
rfc2544throughput_1trial_imix_151323.txt

[beubanks@beubanks-cs9-1 ixia-env]$ ls | grep 131623
rfc2544throughput_1trial_imix_AggregateResults_131623.csv
rfc2544throughput_1trial_imix_iteration_131623.csv
rfc2544throughput_1trial_imix_logFile_131623.txt
rfc2544throughput_1trial_imix_report_131623.pdf
rfc2544throughput_1trial_imix_results_131623.csv
`