(Possibly) fixes#3470
When updating the main file /files_external/rootcerts.crt we should not
read from /files_external/rootcerts.crt at the same time.
For 2 reasons: writing to a file and reading from it at the same time
can have non deterministic results
And we don't want all the certificates to appear 2 times in there.
This isn't caught by our standard file locking (that does not allow this
actually) because it is in a non locked path....
Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>
5a61a794d4