ashmem-test: Add a test for setting a buffer's name

Add a test to ensure that the kernel only reads up to the NUL
terminator for a given string and not beyond it.

Bug: 409148925
Bug: 409422661
Bug: 411741996
Change-Id: I360788de38ed28368ca0c6b83786b0c3b7ba7aa3
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>