fio: Bump Git tag to fio-2.7
fio: Bump Git tag to fio-2.7

On modern Linux kernels  fio-2.2.10 fails to build from
source due to missing a header file stdint.h that used to be included in
mtd-user.h. fio-2.7 tag includes the fix for this issue.

For more info on the bug see:
https://github.com/axboe/fio/commit/d7bb6180f831091c468e5aa749b142efd5eddda4

GoogleCloudPlatform/PerfKitBenchmarker,meteorfox/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,GoogleCloudPlatform/PerfKitBenchmarker,meteorfox/PerfKitBenchmarker