Dynamic network test changes (#795)

- No sigverify if feature sigverify_cpu_disable is used
- Purge validators in the test if lag count increases beyond
  SOLANA_DYNAMIC_NODES_PURGE_LAG environment variable
- Other useful log messages in the test

src/sigverify.rs

@@ -6,8 +6,13 @@
 
 use counter::Counter;
 use packet::{Packet, SharedPackets};
+
+#[cfg(not(feature = "sigverify_cpu_disable"))]
 use std::mem::size_of;
+
 use std::sync::atomic::AtomicUsize;
+
+#[cfg(not(feature = "sigverify_cpu_disable"))]
 use transaction::{PUB_KEY_OFFSET, SIGNED_DATA_OFFSET, SIG_OFFSET};
 
 pub const TX_OFFSET: usize = 0;
@@ -42,6 +47,7 @@ pub fn init() {
 }
 
 #[cfg(not(feature = "cuda"))]
+#[cfg(not(feature = "sigverify_cpu_disable"))]
 fn verify_packet(packet: &Packet) -> u8 {
     use ring::signature;
     use signature::{PublicKey, Signature};
@@ -66,6 +72,12 @@ fn verify_packet(packet: &Packet) -> u8 {
     ).is_ok() as u8
 }
 
+#[cfg(feature = "sigverify_cpu_disable")]
+fn verify_packet(_packet: &Packet) -> u8 {
+    warn!("signature verification is disabled");
+    return 1;
+}
+
 fn batch_size(batches: &[SharedPackets]) -> usize {
     batches
         .iter()