main, vmm: seccomp: Add the '--seccomp log' option

This patch extends the CLI option '--seccomp' to accept the 'log'
parameter in addition 'true/false'. It also refactors the
vmm::seccomp_filters module to support both "SeccompAction::Trap" and
"SeccompAction::Log".

Fixes: #1180

Signed-off-by: Bo Chen <chen.bo@intel.com>

src/main.rs

@@ -260,7 +260,7 @@ fn create_app<'a, 'b>(
             Arg::with_name("seccomp")
                 .long("seccomp")
                 .takes_value(true)
-                .possible_values(&["true", "false"])
+                .possible_values(&["true", "false", "log"])
                 .default_value("true"),
         );
 
@@ -292,6 +292,7 @@ fn start_vmm(cmd_arguments: ArgMatches) {
         match seccomp_value {
             "true" => SeccompAction::Trap,
             "false" => SeccompAction::Allow,
+            "log" => SeccompAction::Log,
             _ => {
                 eprintln!("Invalid parameter {} for \"--seccomp\" flag", seccomp_value);
                 process::exit(1);