ANDROID: selftests: incfs: Increase timeout in concurrent_reads_and_writes_test

Increase the default timeout value for concurrent_reads_and_writes_test
to avoid timeout valuse. With timeout value equal to 500ms the test
doesn't timeout on a VM and all functional tests pass.

Bug: 248081692

Signed-off-by: Tadeusz Struk <tadeusz.struk@linaro.org>
Change-Id: I04225cf3c007ed250a29b8d35b6056f97a4957dc