[Update] Add improved error message for buffer allocation failure in HE-MEM

[a-thompson2]

Description

Addresses this case. When not enough/no hugepages are allocated, the memory host exerciser simply fails similar to the following:

    starting test run, count of 1
API version: 2
AFU clock: 470 MHz
Allocate SRC Buffer
    Test mem(1): FAIL

With this change, it instead fails like so, notifying the user that enough hugepages might not be reserved:

    starting test run, count of 1
API version: 2
AFU clock: 470 MHz
Allocate SRC Buffer
SRC Buffer allocation failed. Please check that hugepages are reserved.
    Test mem(1): FAIL

The implementation specifically catches opae::fpga::types::except as that is what gets thrown from the VFIO plugin's fpgaPrepareBuffer implementation when its internal opae_vfio_buffer_mmap call is unsuccessful (such as when there are no hugepages).

Collateral (docs, reports, design examples, case IDs):

Tests added:

Tests run:

Tested manually on n6001

[coveralls]

Pull Request Test Coverage Report for Build 7846720071

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 64.508%

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Totals
Change from base Build 7846576248:	0.0%
Covered Lines:	15809
Relevant Lines:	24507

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💛 - Coveralls