Build Open vSwitch with OpenSSL support

Open vSwitch does not currently build with OpenSSL support due to the
libcrypto libraries not being able to dynamically load other modules.
Set the LIBS build-environment variable to enable dynamic linking during
the build process.

Change-Id: I5145068b00d3056125a6eb11f3c6621352530fae

snapcraft.yaml

@@ -874,6 +874,8 @@ parts:
   openvswitch:
     source: https://github.com/openvswitch/ovs/archive/v2.14.0.tar.gz
     plugin: autotools
+    build-environment:
+      - LIBS: -ldl
     build-packages:
       - autoconf
       - binutils