misc: Eliminate use of assert!((...).is_ok())

Asserting on .is_ok()/.is_err() leads to hard to debug failures (as if
the test fails, it will only say "assertion failed: false". We replace
these with `.unwrap()`, which also prints the exact error variant that
was unexpectedly encountered (we can to this these days thanks to
efforts to implement Display and Debug for our error types). If the
assert!((...).is_ok()) was followed by an .unwrap() anyway, we just drop
the assert.

Inspired by and quoted from @roypat.

Signed-off-by: Ruoqing He <heruoqing@iscas.ac.cn>

arch/src/x86_64/mod.rs

@@ -1581,7 +1581,7 @@ mod tests {
             None,
             None,
         );
-        assert!(config_err.is_err());
+        config_err.unwrap_err();
 
         // Now assigning some memory that falls before the 32bit memory hole.
         let arch_mem_regions = arch_memory_regions();
@@ -1686,13 +1686,13 @@ mod tests {
         // Exercise the scenario where the field storing the length of the e820 entry table is
         // is bigger than the allocated memory.
         params.e820_entries = params.e820_table.len() as u8 + 1;
-        assert!(add_e820_entry(
+        add_e820_entry(
             &mut params,
             e820_table[0].addr,
             e820_table[0].size,
-            e820_table[0].type_
+            e820_table[0].type_,
         )
-        .is_err());
+        .unwrap_err();
     }
 
     #[test]

arch/src/x86_64/mptable.rs

@@ -336,7 +336,7 @@ mod tests {
         let mem = GuestMemoryMmap::from_ranges(&[(MPTABLE_START, compute_mp_size(num_cpus) - 1)])
             .unwrap();
 
-        assert!(setup_mptable(MPTABLE_START, &mem, num_cpus, None).is_err());
+        setup_mptable(MPTABLE_START, &mem, num_cpus, None).unwrap_err();
     }
 
     #[test]
@@ -433,6 +433,6 @@ mod tests {
             GuestMemoryMmap::from_ranges(&[(MPTABLE_START, compute_mp_size(cpus as u8))]).unwrap();
 
         let result = setup_mptable(MPTABLE_START, &mem, cpus as u8, None);
-        assert!(result.is_err());
+        result.unwrap_err();
     }
 }