[COMMON][CERTS] Use sh to onboard custom certs

Today, onboarding custom certificates relies on `bash`. But image used
for that doesn't have bash.
Therefore, we need to use `sh` in order to onboard the certs.

Issue-ID: OOM-2666
Signed-off-by: Sylvain Desbureaux <sylvain.desbureaux@orange.com>
Change-Id: Ia8087bd9484a013ac76044681059f634a4e45eb8
2 files changed