Interactive account passwords (#1623)

## Issue Addressed

#1437

## Proposed Changes

- Make the `--wallet-password` flag optional and creates an interactive prompt if not provided.
- Make the `--wallet-name` flag optional and creates an interactive prompt if not provided.
- Add a minimum password requirement of a 12 character length.
- Update the `--stdin-passwords` flag to `--stdin-inputs` because we have non-password user inputs 

## Additional Info

common/account_utils/src/lib.rs

@@ -17,6 +17,8 @@ pub mod validator_definitions;
 pub use eth2_keystore;
 pub use eth2_wallet::PlainText;
 
+/// The minimum number of characters required for a wallet password.
+pub const MINIMUM_PASSWORD_LEN: usize = 12;
 /// The `Alphanumeric` crate only generates a-z, A-Z, 0-9, therefore it has a range of 62
 /// characters.
 ///
@@ -108,7 +110,7 @@ pub fn read_password_from_user(use_stdin: bool) -> Result<ZeroizeString, String>
 }
 
 /// Reads a mnemonic phrase from TTY or stdin if `use_stdin == true`.
-pub fn read_mnemonic_from_user(use_stdin: bool) -> Result<String, String> {
+pub fn read_input_from_user(use_stdin: bool) -> Result<String, String> {
     let mut input = String::new();
     if use_stdin {
         io::stdin()
@@ -121,9 +123,33 @@ pub fn read_mnemonic_from_user(use_stdin: bool) -> Result<String, String> {
             .read_line(&mut input)
             .map_err(|e| format!("Error reading from tty: {}", e))?;
     }
+    trim_newline(&mut input);
     Ok(input)
 }
 
+fn trim_newline(s: &mut String) {
+    if s.ends_with('\n') {
+        s.pop();
+        if s.ends_with('\r') {
+            s.pop();
+        }
+    }
+}
+
+/// Takes a string password and checks that it meets minimum requirements.
+///
+/// The current minimum password requirement is a 12 character length character length.
+pub fn is_password_sufficiently_complex(password: &[u8]) -> Result<(), String> {
+    if password.len() >= MINIMUM_PASSWORD_LEN {
+        Ok(())
+    } else {
+        Err(format!(
+            "Please use at least {} characters for your password.",
+            MINIMUM_PASSWORD_LEN
+        ))
+    }
+}
+
 /// Provides a new-type wrapper around `String` that is zeroized on `Drop`.
 ///
 /// Useful for ensuring that password memory is zeroed-out on drop.
@@ -146,6 +172,7 @@ impl AsRef<[u8]> for ZeroizeString {
 
 #[cfg(test)]
 mod test {
+    use super::is_password_sufficiently_complex;
     use super::strip_off_newlines;
 
     #[test]
@@ -181,4 +208,20 @@ mod test {
             expected
         );
     }
+
+    #[test]
+    fn test_password_over_min_length() {
+        is_password_sufficiently_complex(b"TestPasswordLong").unwrap();
+    }
+
+    #[test]
+    fn test_password_exactly_min_length() {
+        is_password_sufficiently_complex(b"TestPassword").unwrap();
+    }
+
+    #[test]
+    #[should_panic]
+    fn test_password_too_short() {
+        is_password_sufficiently_complex(b"TestPass").unwrap();
+    }
 }