TT#29620 Clean shellcheck TAP test warning: SC2046 and SC2006

Fixed the following warnings:
 * Use $(..) instead of deprecated `..` [SC2006]
 * Quote this to prevent word splitting. [SC2046]

Also make it more readable.

Change-Id: Ib070dc31a320700ff0ec41e4d90a0586da9551f1

script/ssl-server.sh

@@ -1,2 +1,13 @@
 #!/bin/sh
-CATALYST_DEBUG=1 DBIC_TRACE=1 DBIC_TRACE_PROFILE=console DEVEL_CONFESS_OPTIONS='objects builtin dump color source' perl `which plackup` -I ../data-hal/lib -I ../ngcp-schema/lib -I lib -I ../sipwise-base/lib/ ngcp_panel.psgi --listen /tmp/ngcp_panel_sock --nproc 1 -s FCGI -r
+
+export CATALYST_DEBUG=1
+export DBIC_TRACE=1
+export DBIC_TRACE_PROFILE=console
+export DEVEL_CONFESS_OPTIONS='objects builtin dump color source'
+
+perl "$(which plackup)" \
+  -I ../data-hal/lib \
+  -I ../ngcp-schema/lib \
+  -I lib \
+  -I ../sipwise-base/lib/ \
+  ngcp_panel.psgi --listen /tmp/ngcp_panel_sock --nproc 1 -s FCGI -r