Fix process-related metrics collection feature

Previously, it wasn't enabled when building with:
```
cargo build --all --features "prometheus/process" --release
```

Cargo.lock

@@ -1,5 +1,11 @@
 # This file is automatically @generated by Cargo.
 # It is not intended for manual editing.
+[[package]]
+name = "adler"
+version = "1.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f26201604c87b1e01bd3d98f8d5d9a8fcbb815e8cedb41ffccbeb4bf593a35fe"
+
 [[package]]
 name = "aho-corasick"
 version = "0.7.18"
@@ -243,6 +249,15 @@ dependencies = [
  "void",
 ]
 
+[[package]]
+name = "crc32fast"
+version = "1.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "81156fece84ab6a9f2afdb109ce3ae577e42b1228441eded99bd77f627953b1a"
+dependencies = [
+ "cfg-if 1.0.0",
+]
+
 [[package]]
 name = "crossbeam-channel"
 version = "0.5.1"
@@ -374,6 +389,18 @@ dependencies = [
  "termcolor",
 ]
 
+[[package]]
+name = "flate2"
+version = "1.0.22"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e6988e897c1c9c485f43b47a529cef42fde0547f9d8d41a7062518f1d8fc53f"
+dependencies = [
+ "cfg-if 1.0.0",
+ "crc32fast",
+ "libc",
+ "miniz_oxide",
+]
+
 [[package]]
 name = "fmt2io"
 version = "0.1.0"
@@ -428,6 +455,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "hex"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f24254aa9a54b5c858eaee2f5bccdb46aaf0e486a595ed5fd8f86ba55232a70"
+
 [[package]]
 name = "humantime"
 version = "1.3.0"
@@ -560,6 +593,16 @@ dependencies = [
  "autocfg 1.0.1",
 ]
 
+[[package]]
+name = "miniz_oxide"
+version = "0.4.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a92518e98c078586bc6c934028adcca4c92a53d6a958196de835170a01d84e4b"
+dependencies = [
+ "adler",
+ "autocfg 1.0.1",
+]
+
 [[package]]
 name = "nom"
 version = "5.1.2"
@@ -657,6 +700,20 @@ dependencies = [
  "unicode-xid",
 ]
 
+[[package]]
+name = "procfs"
+version = "0.10.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "95e344cafeaeefe487300c361654bcfc85db3ac53619eeccced29f5ea18c4c70"
+dependencies = [
+ "bitflags",
+ "byteorder",
+ "flate2",
+ "hex",
+ "lazy_static",
+ "libc",
+]
+
 [[package]]
 name = "prometheus"
 version = "0.13.0"
@@ -666,8 +723,10 @@ dependencies = [
  "cfg-if 1.0.0",
  "fnv",
  "lazy_static",
+ "libc",
  "memchr",
  "parking_lot",
+ "procfs",
  "protobuf",
  "thiserror",
 ]

Cargo.toml

@@ -15,6 +15,7 @@ build = "build.rs"
 [features]
 default = ["metrics"]
 metrics = ["prometheus", "tiny_http"]
+metrics_process = ["prometheus/process"]
 
 [package.metadata.configure_me]
 spec = "internal/config_specification.toml"

server.sh

@@ -3,7 +3,7 @@ set -eux
 cd `dirname $0`
 
 cargo fmt --all
-cargo build --all --features "prometheus/process" --release
+cargo build --all --features "metrics_process" --release
 
 NETWORK=$1
 shift

src/metrics.rs

@@ -2,7 +2,7 @@
 mod metrics_impl {
     use anyhow::{Context, Result};
 
-    #[cfg(feature = "prometheus/process")]
+    #[cfg(feature = "metrics_process")]
     use prometheus::process_collector::ProcessCollector;
 
     use prometheus::{self, Encoder, HistogramOpts, HistogramVec, Registry};
@@ -20,7 +20,7 @@ mod metrics_impl {
         pub fn new(addr: SocketAddr) -> Result<Self> {
             let reg = Registry::new();
 
-            #[cfg(feature = "prometheus/process")]
+            #[cfg(feature = "metrics_process")]
             reg.register(Box::new(ProcessCollector::for_self()))
                 .expect("failed to register ProcessCollector");