gerrit-sshd: Remove usages of Throwables#propagate

Change Ic0e0819b5 added some calls to Throwables#propagate, but I
overlooked that previously existing usages had been replaced in
change Id148cb961 due to intention of Guava to deprecate it.

Change-Id: I90e513c85da4fecbe22679ebbf45badbf3a9edde

gerrit-sshd/src/main/java/com/google/gerrit/sshd/AliasCommand.java

@@ -99,7 +99,8 @@ public class AliasCommand extends BaseCommand {
       try {
         cmd.destroy();
       } catch (Exception e) {
-        Throwables.propagate(e);
+        Throwables.propagateIfPossible(e);
+        throw new RuntimeException(e);
       }
     }
   }

gerrit-sshd/src/main/java/com/google/gerrit/sshd/DispatchCommand.java

@@ -137,7 +137,8 @@ final class DispatchCommand extends BaseCommand {
       try {
         cmd.destroy();
       } catch (Exception e) {
-        Throwables.propagate(e);
+        Throwables.propagateIfPossible(e);
+        throw new RuntimeException(e);
       }
     }
   }

gerrit-sshd/src/main/java/com/google/gerrit/sshd/SuExec.java

@@ -155,7 +155,8 @@ public final class SuExec extends BaseCommand {
       try {
         cmd.destroy();
       } catch (Exception e) {
-        Throwables.propagate(e);
+        Throwables.propagateIfPossible(e);
+        throw new RuntimeException(e);
       }
     }
   }