output file creation fails due to full path prepended to file name

[derekbruening]

After resolving issue #2, we have an output failure creation error due to prepending the full path and thus producing a directory that does not exist:

$ ./roofline.py record /mypath/dr/test/roofline 1 100000
/mypath/extsw/roofline//dynamorio/build/bin64/drrun  -c /mypath/extsw/roofline//client/build/libroofline.so --output_folder /mypath/extsw/roofline//mypath/dr/test/roofline_1_1000002021-05-11_02:24:21/       -- /mypath/dr/test/roofline 1 100000
> Roofline is running to get FP and Bytes accessed.
<wrapping _RoiStart @0x00007ff57b900275
<wrapping _RoiEnd @0x00007ff57b900287
Estimation of pi is 3.141592653598162
Received 29 alarms
/mypath/extsw/roofline//dynamorio/build/bin64/drrun  -c /mypath/extsw/roofline//client/build/libroofline.so --output_folder /mypath/extsw/roofline//mypath/dr/test/roofline_1_1000002021-05-11_02:24:21/       --time_run -- /mypath/dr/test/roofline 1 100000
> Roofline is running for gathering timining information
<wrapping _RoiStart @0x00007f0eafb67275
<wrapping _RoiEnd @0x00007f0eafb67287
Estimation of pi is 3.141592653598162
Received 2 alarms

$ ./roofline.py report -i mypath/dr/test/roofline_1_1000002021-05-11_02\:24\:21 --line myhost_FP64 --output_dir out
Roofline: building report merging a roofline for myhost_FP64 precision. Please make sure you target application has used the same precision
Opening mypath/dr/test/roofline_1_1000002021-05-11_02:24:21//mypath/dr/test/roofline_1_100000.dat
Traceback (most recent call last):
  File "/mypath/extsw/roofline/./roofline.py", line 695, in <module>
    sys.exit(main())
  File "/mypath/extsw/roofline/./roofline.py", line 691, in main
    args.func(args)
  File "/mypath/extsw/roofline/./roofline.py", line 455, in report
    create_dat_file(in_dir, get_app_title(in_dir), current_points)
  File "/mypath/extsw/roofline/./roofline.py", line 101, in create_dat_file
    f = open(out_file, "w+")
FileNotFoundError: [Errno 2] No such file or directory: 'mypath/dr/test/roofline_1_1000002021-05-11_02:24:21//mypath/dr/test/roofline_1_100000.dat'