cmdline app: add provider commandline options.

Add a -provider option to allow providers to be loaded. This option can be
specified multiple times.

Add a -provider_path option to allow the path to providers to be specified.

Reviewed-by: Tomas Mraz <tmraz@fedoraproject.org>
(Merged from https://github.com/openssl/openssl/pull/11167)

apps/nseq.c

diff --git a/apps/nseq.c b/apps/nseq.c
index 9d1e095..e9aeea9 100644
--- a/apps/nseq.c
+++ b/apps/nseq.c
@@ -16,7 +16,8 @@
 
 typedef enum OPTION_choice {
     OPT_ERR = -1, OPT_EOF = 0, OPT_HELP,
-    OPT_TOSEQ, OPT_IN, OPT_OUT
+    OPT_TOSEQ, OPT_IN, OPT_OUT,
+    OPT_PROV_ENUM
 } OPTION_CHOICE;
 
 const OPTIONS nseq_options[] = {
@@ -29,6 +30,8 @@
     OPT_SECTION("Output"),
     {"toseq", OPT_TOSEQ, '-', "Output NS Sequence file"},
     {"out", OPT_OUT, '>', "Output file"},
+
+    OPT_PROV_OPTIONS,
     {NULL}
 };
 
@@ -62,6 +65,10 @@
         case OPT_OUT:
             outfile = opt_arg();
             break;
+        case OPT_PROV_CASES:
+            if (!opt_provider(o))
+                goto end;
+            break;
         }
     }
     argc = opt_num_rest();