Increase storage blockdevice Unittest coverage

[rajkan01]

Description of defect

Summarized the test coverage data in a table:	Blockdevice	% covered	Refer to Unit under test	Missing
BufferedBlockDevice.cpp	89	index.storage_blockdevice_source_BufferedBlockDevice.cpp.htm.pdf	48,53,83,89,104,110,132,162,186,216,241,254,259,295-296,299-300,302
ChainingBlockDevice.cpp	82	index.storage_blockdevice_source_ChainingBlockDevice.cpp.htm.pdf	42,58,65,72,79,95-98,104,110,116,130-133,137,147,164,185,202,219,223,238,282
HeapBlockDevice.cpp	97.8	index.storage_blockdevice_source_HeapBlockDevice.cpp.html.pdf	62,165
ExhaustibleBlockDevice.cpp	87	index.storage_blockdevice_source_ExhaustibleBlockDevice.cpp..pdf	40,45,59-62,74,89,98,138,209
FlashSimBlockDevice.cpp	89	index.storage_blockdevice_source_FlashSimBlockDevice.cpp.htm.pdf	54,59,71-74,86,153,174,210,230
MBRBlockDevice.cpp	86	index.storage_blockdevice_source_MBRBlockDevice.cpp.html.pdf	84,92-93,101-103,112-114,154-155,161-162,174,182,189,194,205,220,225,248,253,262,298-299,322,335,453
ObservingBlockDevice.cpp	93	index.storage_blockdevice_source_ObservingBlockDevice.cpp.ht.pdf	49,51,115
ReadOnlyBlockDevice.cpp	15	index.storage_blockdevice_source_ReadOnlyBlockDevice.cpp.htm.pdf	37,39,42,44,47,49,52,54,57,59,62,64,67,69,72,74,77,79,82,84,87,89,92,94,97,99-100,103
ProfilingBlockDevice.cpp	98	index.storage_blockdevice_source_ProfilingBlockDevice.cpp.ht.pdf	131
SlicingBlockDevice.cpp	98	index.storage_blockdevice_source_SlicingBlockDevice.cpp.html.pdf	51
SFDP.cpp	6	index.storage_blockdevice_source_SFDP.cpp.html.pdf	35,37,41,43,87,89,91,96,99,107,109,111,114,117,120-121,125-128,130-133,135-137,139,141-142,144-145,147-148,150-151,153-154,156-157,159-160,162-163,165-166,181,184,186-187,191,194-195,197,200-202,206,209,215-217,219,222-224,227,231,234,236,238,240,243-244,246,248,257-258,260,265-266,268,272,274,277-278,282,287-289,291,293,295,297,301,303-307,309,312,315,317-318,320,322,324-325,330,333,335,338,340-343,346,348-349,351-352,354,356,361,366-367,369,373,376,378-379,382-383,386,388-389,392,423,426-430,432,436,450,453-454,457

Target(s) affected by this defect ?

N/A

Toolchain(s) (name and version) displaying this defect ?

N/A

What version of Mbed-os are you using (tag or sha) ?

Latest

What version(s) of tools are you using. List all that apply (E.g. mbed-cli)

N/A

How is this defect reproduced ?

View test coverage report

[ciarmcom]

Thank you for raising this detailed GitHub issue. I am now notifying our internal issue triagers. Internal Jira reference: https://jira.arm.com/browse/IOTOSM-3951