provider/boltmem: properly compare timestamps
provider/boltmem: properly compare timestamps

Depending on the environment the timestamp internal fields
are different to handle timezones.
Thus a reflect.DeepEqual comparison falsely evaluates to
false.
This commit manually compares timestamps via the time.Time.Equal
method to circumvent the issue.

brunoqc/alertmanager,tinytub/alertmanager,tyrken/alertmanager,sarathsp06/alertmanager,Aloomaio/alertmanager,brunoqc/alertmanager,Aloomaio/alertmanager,brunoqc/alertmanager,Kellel/alertmanager,tinytub/alertmanager,brancz/alertmanager,tyrken/alertmanager,sarathsp06/alertmanager,joehandzik/alertmanager,prometheus/alertmanager,prometheus/alertmanager,GoogleCloudPlatform/alertmanager,GoogleCloudPlatform/alertmanager,tyrken/alertmanager,joehandzik/alertmanager,brancz/alertmanager,GoogleCloudPlatform/alertmanager,prometheus/alertmanager,Aloomaio/alertmanager,sarathsp06/alertmanager,brancz/alertmanager,tbouvet/alertmanager,tbouvet/alertmanager,tinytub/alertmanager,tbouvet/alertmanager,prometheus/alertmanager,tyrken/alertmanager,ericgerling/alertmanager,GoogleCloudPlatform/alertmanager,brunoqc/alertmanager,ericgerling/alertmanager,ericgerling/alertmanager,Kellel/alertmanager,Kellel/alertmanager,joehandzik/alertmanager,brancz/alertmanager