test: fix util_pool_create running on tmpfs file system

Fix the util_pool_create unit test so that it does not fail
when running on the tmpfs file system.
vmem: unlock arena->lock when returning from READ/WRITE macros
Merge pull request #68 from ldorau/test-fix-util_pool_create

test: fix util_pool_create running on tmpfs file system
Merge pull request #69 from krzycz/vmem-arena_lock

vmem: unlock arena->lock when returning from READ/WRITE macros