DO NOT MERGE Add sleep(3) after stopSupplicant when VtsHalWifiSupplicant

[root cause  ] VtsHalWifiSupplicant first stop supplicant, but framework will restart supplicant, the test will fail, according to Partner IssueTracker 169498893, AOSP suggest to add a blocking
[changes     ] add sleep(3)
[side effects]no
[self test   ]:yes
[download normally]:yes
[power on/off normally]:yes
[do common repository/branch inspection]:no
[is there dependence]:no
[confirm dependent commit]:no
[board]:unisoc
[test case]:VtsHalWifiSupplicant test
[reviewers   ] chao.meng
[change_type ] feature_bugfix
[tag_product ] common

Bug: 169498893
Change-Id: I7990226d346a3444f606951386e7c223fc87f98f