snap: fix username lookup over https and likely some other tls uses

Without libssl-dev available in build time, we would fall back on
building our own from a locally-built libressl, which would have
incorrect paths for location of certificates: the resulting snap
would incorrectly try to look for certificates under
parts/jami/build/daemon/contrib/x86_64-linux-gnu/etc/ssl, which is
not available after build, instead of a more sensible /etc/ssl.

Change-Id: I76cb847d18561e29250d4b9d39d1993dabc9a864